Introduction to molds（1）
1 Introduction
1.1 The Big Picture
When the Hyatt brothers, John and Isaiah, built and patented the first injection moulding machine in
1872, it is doubtful if they could possibly have imagined the impact this invention would have on the
world. It spawned a worldwide industry employing approximately 0.5 million workers in the US alone.
‘Miscellaneous plastics products’ which also includes other plastic manufacturing industries such as
extrusion, is the 4th largest manufacturing industry in the US. In 2001, it was estimated that there were
21,000 operating plastics industry establishments in the US, generating approximately $321 billion in
shipments. If upstream, supplying industries are also included, this total annual shipment is nearly $409
billion. The smaller UK plastics sector by comparison is worth £18 billion annually.
In Western Europe the consumption of thermoplastic materials alone in 2002 was around 33 million
tonnes. Of this, engineering resins reached a market size of around 2.5 million tonnes. The country to
country usage of materials varies widely, for example Italy is the largest consumer of unsaturated
polyester resins in Europe consuming 23% of the European market demand in 2002. 27% of all plastic
consumed is used by injection moulders. The biggest injection moulding industry of all the European
countries is found in Germany which not surprisingly therefore uses the most raw material.
The packaging sector accounts for about 24% of this market, with the automotive industry 18% and the
electrical equipment industry 18%. Other important markets for plastics materials are the construction
industry and consumer products.
A major factor for the entire injection moulding industry has been the globalisation of the market. The
manufacturing base for many plastic injection mouldings has moved to low cost plants such as those
found in China, India and Eastern Europe. To adapt to the increased competition, Western
manufacturers have moved into more technically difficult products and mouldings, as well as
developing the markets into more advanced processes such as those that will be discussed in Chapter
10.
From these few facts and figures it can be seen that injection moulding is an extremely large and
important manufacturing industry, but what is injection moulding?
1.2 Introduction to Injection Moulding
Injection moulding is one of the most common processes used to produce plastic parts. It is a cyclic
process of rapid mould filling followed by cooling and ejection. A variety of materials both plastic and
non-plastic can be used as feedstock. However, the machine must be configured for the type of material
used.
The material, which is generally available as grains or powder, is plasticised in an injection unit and
injected into a clamped mould under high pressure (500-1500 bar). The main advantage of injection
moulding is that it is a very economical method of mass production. Ready parts with tight tolerances
can be produced in one step, often completely automatically. In general after-processing is not
necessary. It is also possible to integrate different functions into one part to avoid the formation of
different components that would be more expensive, e.g., the base of a typewriter with integrated
guidance and fixing elements, the springy components of a printer element, a lens with integrated
prisma to stop down a beam of light.
To guarantee a high quality in the injection moulded parts the following points have to be considered:
• The material has to be plasticised and injected carefully to avoid negative effects on the material
properties.
• The process settings (such as pressures and temperatures) concerning the machine and mould have
to remain constant with regard to time and space.
• Basic parts of an injection moulding machine.
An example of a commercially available injection moulding machine is shown in Figure 1.1. The basic
parts that make up a machine are shown in Figure 1.2.
